This invention relates to liquid ring pumps, and more particularly to liquid ring pumps having conical or cylindrical port members.
A liquid ring pump having conical port members is shown in Jennings U.S. Pat. No. 3,154,240. The principal components of this pump are (1) a cylindrical housing: (2) a rotatable shaft mounted eccentrically in the housing; (3) a bladed rotor fixedly mounted on the shaft; (4) two frusto-conical port members coaxial with the shaft, each port member extending into an annular recess in a respective one of the opposite ends of the rotor and having (a) an intake port for admitting to the rotor the gas, vapor, or gas-vapor mixture to be pumped (hereinafter referred to generically as gas) and (b) a discharge port for conveying compressed gas from the rotor; and (5) a head member at each end of the pump for conveying gas between the associated port member and appropriate pump inlets and outlets. Although the port members shown in the above-mentioned Jennings patent are frusto-conical, those skilled in the art frequently refer to them as conical, and that terminology is accordingly employed herein. Those skilled in the art will also appreciate that the port members in the Jennings device need not be tapered in the manner of a cone, but could alternatively be cylindrical, in which case the pump would be referred to as cylindrically ported.
Returning to the Jennings device, a quantity of pumping liquid (e.g., water) is maintained in the housing. When the shaft and rotor are rotated, the rotor blades engage the pumping liquid and form it into an annular ring concentric with the housing. The liquid ring cooperates with the rotor blades to form a plurality of gas pumping chambers, each chamber being bounded by (1) two adjacent rotor blades, (2) the adjacent portion of the rotor hub or the conical port member, and (3) the adjacent portion of the inner surface of the liquid ring. Because the rotor is eccentric to the housing, these pumping chambers vary in size in a cyclic fashion as the rotor rotates. On the side of the pump in which the rotor blades are diverging from the housing, the pumping chambers are expanding. This is the gas intake zone of the pump, and the intake ports are therefore located so as to communicate with the pumping chambers in this zone. On the side of the pump in which the rotor blades are converging toward the housing, the pumping chambers are contracting. This is the gas compression zone of the pump, and the discharge ports are therefore located so as to communicate with the pumping chambers in this zone.
Liquid ring pumps are typically designed to provide a particular compression ratio or a relatively narrow range of compression ratios for extended periods of time. When a liquid ring pump is subjected to off-normal operating conditions, the power required to operate the pump may increase substantially. For example, when a liquid ring pump is being started and the compression ratio is lower than normal, very high pressures may occur in the compression zone of the pump prior to the discharge port. This overcompression of the gas being pumped increases the power necessary to drive the pump until the normal compression ratio is achieved. In order to meet these occasional increased power requirements, the pump must be equipped with a motor larger than would otherwise be necessary. This is uneconomical, and it is clearly desirable to minimize the amount by which the power requirements of the pump increase under off-normal operating conditions.
Another consideration in the design of liquid ring pumps is that the higher the compression ratio the pump is designed to achieve, the more sensitive the pump becomes to off-normal operating conditions. Typically, if a liquid ring pump is designed to achieve a very high compression ratio, it is subject to very severe overcompression problems at lower than normal compression ratios. Similarly, unless a liquid ring pump is designed to achieve a high compression ratio (in which case it typically operates less efficiently at lower compression ratios), it generally cannot achieve such high compression ratios at all.
Still another characteristic of liquid ring pumps, especially those designed for operation at relatively low speeds and low compression ratios, is that such pumps may exhibit instability manifested by excessive vibration and loss of pumping ability when subjected to compression ratios higher than the design compression ratio. This condition may be ameliorated by increasing the flow of pumping liquid to the pump. But this approach usually increases pump operating cost and and may only shift the point at which the pump becomes unstable.
In view of the foregoing, it is an object of this invention to improve liquid ring pumps of the type described above.
It is another object of this invention to provide liquid ring pumps of the type described above which operate efficiently over relatively broad compression ratio ranges.
It is yet another object of this invention to provide liquid ring pumps of the type described above which are capable of achieving relatively high compression ratios without excessive inefficiency at lower compression ratios.
It is still another object of this invention to increase the stability of operation of liquid ring pumps of the type described above without increasing the rate at which pumping liquid must be supplied to the pump.
It is yet another object of this invention to increase the efficiency of liquid ring pumps of the type described above by permitting operation at lower speeds with reduced risk of instability.
It is still another object of this invention to reduce the rate of pumping liquid consumption in liquid ring pumps of the type described above.